The present invention pertains to microlithographic projection-exposure methods and apparatus for use principally in the manufacture of semiconductor integrated circuits and display devices. In such methods and apparatus, a pattern for a circuit or display array is defined by a reticle or the like and is projected onto a semiconductor wafer or other suitable substrate using an energy beam so as to transfer the pattern to the substrate.
In conventional projection-microlithographic techniques, a pattern (e.g., for a semiconductor chip or display device) is defined on a reticle or other suitable xe2x80x9coriginal platexe2x80x9d. At least a portion of the reticle is illuminated using an energy beam. As the energy beam passes through the reticle, the beam carries an image of the illuminated portion. The image is focused onto a corresponding region of a suitable substrate (termed herein a xe2x80x9cwaferxe2x80x9d). The wafer is normally coated with an appropriate resist that is imprinted with the projected image.
As used herein, xe2x80x9cthroughputxe2x80x9d means the number of wafers, product devices, or other product units that can be manufactured per unit time using the subject method or apparatus; a xe2x80x9cpattern originalxe2x80x9d is a plate, film, or the like that defines a pattern to be transferred to a substrate and encompasses masks, reticles, and analogous structures; an xe2x80x9cenergy beamxe2x80x9d is a medium used to transfer an image of the pattern from the pattern original to the substrate and encompasses visible light, ultraviolet light, X-rays, electron beam, and ion beam; and a xe2x80x9ccharged particle beamxe2x80x9d can be an electron beam, ion beam, or analogous beam. Hence, an xe2x80x9coptical systemxe2x80x9d as referred to herein is not limited to an optical system for light (e.g., visible light, ultraviolet light, X-rays), but also encompasses optical systems for a charged particle beam.
As used herein, a xe2x80x9cfield of viewxe2x80x9d of an optical system or the like is, unless otherwise specified, an imaging region in which aberrations are within specification.
At present, projection-microlithographic exposures made in the mass-production of semiconductor chips are mainly performed using a xe2x80x9cstepperxe2x80x9d that utilizes visible light or ultraviolet light as the energy beam. As feature sizes have continued to decrease with the need to achieve increasingly higher circuit densities on semiconductor chips and displays, the wavelength of light used as the exposure energy beam in steppers is becoming increasingly shorter. This has placed severe limits on the optical materials that can be used in the optical systems (e.g., illumination-optical systems and projection-optical systems) in contemporary steppers.
Aberrations impose limitations to the field of view of optical systems that must satisfy a requirement for high resolution. I.e., whenever fine features must be transferred with high resolution, optical systems exhibiting excessive aberrations have a field of view that is confined to more paraxial regions compared to otherwise similar optical systems in which aberrations are better corrected.
In addition to demands for increased resolution, there is also a demand for ever larger semiconductor devices. Whereas meeting such demands could be achieved using correspondingly larger optical systems, larger optical systems capable of achieving high resolution are more difficult to manufacture to close tolerances than smaller optical systems. Hence, optical systems tend to have a field of view that is too small to project the entire pattern in one xe2x80x9cshotxe2x80x9d.
Therefore, especially when higher integration densities and/or larger devices are the-goal, exposing the entire pattern simultaneously with a single exposure xe2x80x9cshotxe2x80x9d is impractical. To make exposures in such situations, exposure methods have been derived during which the reticle and the wafer are synchronously scanned as in the so-called xe2x80x9clens-scanningxe2x80x9d methods.
Exposure using a charged particle beam (e.g., electron beam) offers prospects of higher resolution than obtainable using visible or ultraviolet light. Unfortunately, conventional charged-particle-beam (CPB) exposure systems exhibit low throughput because of the impracticality of exposing the entire pattern simultaneously in one exposure xe2x80x9cshotxe2x80x9d. Various approaches have been devised to increase throughput of such systems. One conventional approach is termed xe2x80x9ccell projectionxe2x80x9d which involves combining exposures of limited types of pattern portions. (This technique is also termed a xe2x80x9ccharacter projectionxe2x80x9d method.) Unfortunately, this method exhibits a throughput that is inadequate for practical use in the mass-production of semiconductor chips.
Another conventional approach is a xe2x80x9creductionxe2x80x9d (i.e., producing a demagnified image on the wafer relative to the pattern on the reticle) projection-exposure method utilizing an electron beam. This method is disclosed, e.g., in Japanese Kokai patent document no. JP H05-160012. To increase throughput, an electron beam irradiates a reticle defining a circuit pattern for one entire semiconductor chip (i.e., an entire xe2x80x9cdiexe2x80x9d). A demagnified image of the die pattern is transferred to the wafer using a projection lens. In most instances, an extremely large projection-lens field would be required to simultaneously projection-expose the entire die in a single shot. Unfortunately, aberration control over such a large field of view is extremely difficult to achieve with CPB optical systems. Hence, exposure is normally performed by dividing the pattern on the reticle into multiple pattern portions. The pattern portions are successively transferred in an ordered manner from the reticle to the wafer. During each exposure, one or more parameters of the charged particle beam can be changed as required to obtain the best aberration reduction for each exposure. The images on the wafer are xe2x80x9cstitchedxe2x80x9d together by appropriate positioning during exposure to form the entire reticle pattern on the wafer. Certain methods utilizing this approach are termed xe2x80x9cstep-and-scanxe2x80x9d methods or xe2x80x9cdividedxe2x80x9d projection-transfer methods, as disclosed, for example, in U.S. Pat. No. 5,260,151.
Currently, CPB projection-exposure apparatus for mass production utilizing the xe2x80x9cstep-and-scanxe2x80x9d method are not generally available. Also, CPB projection-exposure apparatus utilizing xe2x80x9cdividedxe2x80x9d projection-transfer methods are still in development. In any event, utilizing such methods for forming a plurality of semiconductor chips on a wafer typically requires that the reticle stage be moved over distances (each separate movement consuming a certain amount of time) that prohibit the attainment of satisfactory throughput levels.
Certain types of scanning-type exposure apparatus for mass production are currently available in which the reticle stage exhibits one-dimensional movement. With such apparatus, changing the scanning direction for various die patterns can be performed. However, stitching together of portions of a die pattern as projected onto the wafer to form larger chips has not yet been practicably realized.
In view of the shortcomings of conventional technology as summarized above, an object of the present invention is to provide projection-exposure methods and apparatus that exhibit improved throughput. Such an object is achieved by certain improvements in the manner in which the reticle stage and wafer stage (on which the reticle and wafer, respectively, are mounted during exposure) undergo movement during exposure.
According to a first aspect of the invention, methods are provided for projection-exposing a die pattern, defined by a pattern original and comprising multiple pattern portions for individual exposure, onto multiple locations on a substrate. According to a representative embodiment of such a method, an energy beam is directed to impinge on a pattern portion of the die pattern defined by the pattern original, and to form a patterned beam from the energy beam passing through and propagating downstream of the illuminated pattern portion. (The patterned beam carries an image of the illuminated pattern portion.) The patterned beam is directed to form the image of the illuminated pattern portion on the substrate. This scheme is repeated, in a first exposure order, as required for each of the remaining pattern portions of the die pattern so as to expose an image, comprising stitched-together images of the pattern portions, of the die pattern at a first location on the substrate. Upon transitioning to the next location on the substrate on which the die pattern is to be formed, the foregoing scheme is repeated, but according to a second exposure order that is different (e.g., reversed) from the first exposure order. Thus, an image of the die pattern is exposed at a second location on the substrate.
The pattern original is typically mounted on a first movable stage (i.e., the xe2x80x9cpattern-original stagexe2x80x9d such as a reticle stage) and the substrate is mounted on a second movable stage (i.e., the xe2x80x9csubstrate stagexe2x80x9d) axially displaced from the first movable stage. The first and second stages can be operable to synchronously move the pattern original and substrate, respectively, to scanningly expose each pattern portion. In addition, the first and second stages can be operable to step the pattern original and substrate, respectively, after exposing each pattern portion so as to position the pattern original and substrate, respectively, for exposure of the subsequent pattern portion.
The image of the illuminated pattern portion formed on the substrate is typically a demagnified image. Also, the energy beam can be a beam of electromagnetic radiation such as visible light, ultraviolet light, or X-rays; or a charged particle beam such as an electron beam or ion beam.
The die pattern can be divided into multiple pattern portions arranged on the pattern original. In such an instance, each pattern portion can be sequentially projected, as an exposure unit, and exposed onto the substrate using the energy beam. The pattern original is stepped to a subsequent pattern portion after exposing each pattern portion of the die pattern.
The pattern portions of the die pattern can be arranged in a two-dimensional array on the pattern original. With such an array, the first exposure order can include stepping the pattern original and the substrate in two dimensions so as to expose the die pattern at the first location on the substrate.
The pattern original can remain stationary while the substrate is moved to position the substrate to begin exposure of the die pattern at the second location. Such elimination of certain movements of the pattern original can substantially reduce exposure time per wafer and thus increase throughput.
The energy beam impinging on each pattern portion of the pattern original typically passes through an illumination optical system having a field of view. The die pattern on the pattern original can then be divided into multiple pattern portions each falling within the field of view. With such a scheme, each pattern portion can be sequentially projected, within the field of view, and exposed onto the substrate using the energy beam. The pattern original is stepped to a subsequent pattern portion and the substrate is stepped to a subsequent exposure location for the subsequent pattern portion after exposing each pattern portion of the die pattern.
Alternatively, the die pattern on the pattern original can be divided into multiple pattern portions each having a dimension greater than a corresponding dimension of the field of view. In such an instance, the pattern original and the substrate can be synchronously scanned during exposure of each pattern portion. The pattern original and the substrate are stepped during each transition from exposure of one pattern portion to exposure of a subsequent pattern portion of the die pattern. In the second exposure order, exposure of the pattern portions of the die pattern is performed according to an order that can be opposite the first exposure order. Also, scanning exposure of each pattern portion can be in a direction opposite a direction in which scanning exposure was performed of the corresponding pattern portion in the first exposure order.
The energy beam can be passed through an illumination optical system that directs the energy beam to impinge on each pattern portion, and the patterned beam can be passed through a projection-optical system that directs the patterned beam to corresponding exposure regions on the substrate. In such an instance, the pattern original can be mounted on a first movable stage and the substrate can be mounted on a second movable stage axially displaced from the first movable stage. The first and second stages synchronously move the pattern original and substrate, respectively, as required to expose each pattern portion. If the energy beam is a charged particle beam, the illumination-optical system directs the charged particle beam and the projection-optical system directs the patterned beam and forms an image of the illuminated pattern portion by one or more of electrical and magnetic action that deflects the charged particle beam. Deflection of the charged particle beam on the pattern original and deflection of the patterned beam on the substrate are performed in coordination with movement of the first and second movable stages.
The methods according to the invention include methods in which, whenever a pattern portion is projected outside the substrate, actual exposure of the pattern portion is omitted.
According to another aspect of the invention, projection-exposure apparatus are provided. A representative embodiment of such an apparatus comprises the following: a movable substrate stage on which a substrate is mounted for exposure, a movable pattern-original stage on which a pattern original is mounted for exposure, an illumination optical system situated axially upstream of the pattern-original stage, a projection-optical system situated between the pattern-original stage and the substrate stage, and a controller. The pattern original defines a die pattern to be transferred to multiple locations on the substrate, wherein the die pattern is divided into multiple pattern portions. The pattern-original stage is situated axially downstream of the substrate stage. The illumination-optical system has a field of view and is operable to direct an energy beam so as to illuminate a pattern portion aligned with the field of view. The projection-optical system is operable to form, from the energy beam passing through an illuminated pattern portion, a patterned beam that forms a demagnified image of the illuminate pattern portion on a corresponding exposure region on the substrate. The controller is connected to and operable to controllably operate the illumination-optical system, the pattern-original stage, the projection-optical system, and the substrate stage. The controller is programmed with a map providing the controller with operability to move the pattern-original stage and the substrate stage in at least one of a scanning and step-wise manner so as to sequentially illuminate the pattern portions on the pattern original. The map also provides the controller with operability to control the demagnifying projection of the pattern portions onto corresponding exposure regions of the substrate according to an exposure order while stitching together images of the pattern portions on the exposure regions to form the die pattern on the substrate. The map also provides the controller with operability to change (e.g., reverse) the exposure order of the pattern portions with every sequentially new die being exposed on the substrate.
As noted above, the energy beam can be a charged particle beam. In such an instance, each of the illumination-optical system and the projection-optical system preferably comprises a respective deflector and respective lens that deflect and form an image, respectively, of the charged particle beam by at least one of electric and magnetic action. Deflection of the charged particle beam to illuminate a pattern portion on the pattern original and deflection of the patterned beam on the substrate can be performed in coordination with movement of the substrate stage and the pattern-original stage.
The die pattern can be divided into multiple pattern portions wider than the field of view. In such an instance, the pattern-original stage and the substrate stage can be operable to scanningly move the pattern original and the substrate, respectively, synchronously during each exposure of a pattern portion, and to steppingly move the pattern-original and the substrate, respectively, during a transition from exposure of a previous pattern portion to a subsequent pattern portion. Upon completion of exposure of each die on the substrate, the exposure order of each pattern portion of the die pattern can be reversed and the scanning direction of each pattern portion of the die pattern can be reversed.
In conventional stitching methods or scanning methods of exposure, by producing a demagnified image on the substrate, the pattern original and substrate undergo controlled movement during exposure of each die pattern. During exposure, the distance over which the pattern original moves is longer than the distance over which the substrate moves. According to the invention, by changing or reversing the exposure order with each new exposure of the die pattern on the substrate, the time required to move the pattern original can be minimized, thereby increasing throughput.
In this specification, the concept of xe2x80x9clinkingxe2x80x9d or xe2x80x9cstitchingxe2x80x9d together images of pattern portions on the substrate encompasses situations in which an image at a certain instant and an image at a subsequent instant are transferred by scanning onto the substrate while suitably overlapping the images.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.